A 2005 study by researchers at Stanford University (USA) tracked 900 adults ages 50 and up for 14 years.  They found that the men and women who routinely exercised were less likely to develop pains in their joints and muscles, as well as rheumatoid arthritis.  Men and women who ran, swam, walked briskly, biked, or did aerobics experienced 25% less joint and muscle pain. The pain-free men and women who engaged in brisk aerobic exercise completed upwards of 6 hours of activity per week.

"There are 1440 minutes in each day, and 30 of them should be devoted to physical activity."  ~ U.S. Centers for Disease Control and Prevention